This study will assess the functioning of drug exposed infants within the context of their unique environments (living with a drug using caretaker) and their own characteristic abilities to adapt. Early measures of the newborns' neurobehavioral and emotional adaptability along with maternal and environmental factors will be related to outcome measures of physiological, behavioral, emotional, and cognitive functioning during the second half of the first year of life. The specific functions targeted include the infants' abilities to regulate their arousal and reactivity to stimulation, and their development of emotional expressivity, attentional capacity, motivation, and visual recognition memory (an early predictor of intellectual functioning). One hundred drug exposed, and one hundred non-exposed full-term newborns will be recruited at delivery. Verification of group classification will be determined by 1) examination of prenatal medical records and 2) meconium analysis. The infants will be tested as newborns and again at 1, 4, 6, 9 and 12 months. Assessments will include measures of neurobehavioral functioning, autonomic regulation and reactivity to stimulation (vagal tone, heart rate and cortisol), emotional regulation during mother-infant interactions, mastery motivation and attention during structured play with mother and examiner, Fagan Test of Infant Intelligence, and Bayley Developmental Scales. Maternal assessments include interviews, questionnaires, and observations for drug history and socio-economic factors, parenting attitudes, home and family environment, psychological and intellectual functioning, and maternal interactive and caretaking behavior.